Component of a substrate support assembly producing localized magnetic fields
A component of a substrate support assembly such as a substrate support or edge ring includes a plurality of current loops incorporated in the substrate support and/or the edge ring. The current loops are laterally spaced apart and extend less than halfway around the substrate support or edge ring with each of the current loops being operable to induce a localized DC magnetic field of field strength less than 20 Gauss above a substrate supported on the substrate support during plasma processing of the substrate. When supplied with DC power, the current loops generate localized DC magnetic fields over the semiconductor substrate so as to locally affect the plasma and compensate for non-uniformity in plasma processing across the substrate.
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Disclosed herein is a component of a substrate support assembly having a plurality of current loops adapted to generate small magnetic fields and compensate for variations during plasma processing of a semiconductor substrate supported on the substrate support assembly. The component can be an edge ring or substrate support such as a tunable electrostatic chuck (ESC) that allows for improved control of critical dimension (CD) uniformity, as well as methods and uses thereof.
BACKGROUNDIn this specification where a document, act or item of knowledge is referred to or discussed, this reference or discussion is not an admission that the document, act or item of knowledge or any combination thereof was at the priority date, publicly available, known to the public, part of common general knowledge, or otherwise constitutes prior art under the applicable statutory provisions; or is known to be relevant to an attempt to solve any problem with which this specification is concerned.
Commonly-owned U.S. Pat. No. 6,921,724 discloses an etch processor for etching a wafer that includes an ESC for holding a wafer and a temperature sensor reporting a temperature of the wafer. The chuck includes a heater controlled by a temperature control system and a temperature sensor is operatively coupled to the temperature control system to maintain the temperature of the ESC at a selectable set-point temperature. A first set-point temperature and a second set-point temperature are selected. The wafer is placed on the chuck and set to the first set-point temperature. The wafer is then processed for a first period of time at the first set-point temperature and for a second period of time at the second set-point temperature.
Commonly-owned U.S. Pat. No. 6,847,014 discloses a ESC for a plasma processor comprising a temperature-controlled base, a thermal insulator, a flat support, and a heater. The temperature-controlled base has a temperature below the desired temperature of a substrate. The thermal insulator is disposed over the temperature-controlled base. The flat support holds a substrate and is disposed over the thermal insulator. A heater is embedded within the flat support and/or disposed on an underside of the flat support and includes a plurality of heating elements that heat a plurality of corresponding heating zones. The power supplied and/or temperature of each heating element is controlled independently.
Commonly-owned U.S. Patent Publication No. 2011/0092072 discloses a heating plate for a substrate support assembly in a semiconductor plasma processing apparatus comprising multiple independently controllable planar heater zones arranged in a scalable multiplexing layout, and electronics to independently control and power the planar heater zones.
Thus, there is a need for a component of a substrate support assembly, such as a substrate support assembly comprising an ESC or edge ring, which is capable of making spatial corrections and/or adjustments to the azimuthal plasma processing rate non-uniformity to correct for film thickness variation, etch chamber induced etch rate non-uniformity and large magnetic field (from plasma generation) induced non-uniformity.
While certain aspects of conventional technologies have been discussed to facilitate disclosure of the invention, Applicant in no way disclaims these technical aspects, and it is contemplated that the claimed invention may encompass or include one or more of the conventional technical aspects discussed herein.
SUMMARYDisclosed herein is a component of a substrate support assembly comprising an edge ring or substrate support incorporating a plurality of current loops which generate small magnetic fields in a plasma during plasma processing of at least one semiconductor substrate. The component creates a localized magnetic field without the need for a permanent magnet or iron core. The magnetic fields are small enough to avoid damage to circuits undergoing processing on the semiconductor substrate but strong enough to affect the plasma so as to increase or decrease localized plasma processing such as etch rates during plasma etching. The spatial adjustments to the localized plasma processing rates can compensate for film thickness variation, chamber non-uniformity and/or magnetic field induced non-uniformity.
During plasma processing such as etching, the current loops can be powered to manipulate the plasma and effect spatial adjustments to an azimuthal plasma to correct for film thickness variation, chamber non-uniformity and/or magnetic field induced non-uniformity.
Precise azimuthal CD control on a substrate by small (e.g., <5° C.) corrections azimuthally to the substrate temperature can address CD uniformity which is sensitive to substrate temperature (e.g., as high as 1 nm/° C.). For example, even with an azimuthally symmetric etch chamber design, film thickness non-uniformity can result in azimuthal etch rate non-uniformity, as regions of substrate with thinner films undergo film clearing faster than other regions on the substrate. Small variabilities in hardware also contribute to azimuthal etch rate non-uniformity (e.g., <1%). Large applied DC magnetic fields (e.g., >20 Gauss), such as those used for plasma generation, can be a source of etch rate non-uniformity in plasma etching. Such a magnetic field induces a force, F, defined by F=E×B (where E is the electric field in the plasma and B is the magnetic field) on electrons in the plasma which results in azimuthal non-uniformity in the plasma during plasma etching, such non-uniformity in the plasma can lead to non-uniformity in the etch rate.
Under operational conditions (e.g., plasma etching), DC magnetic fields used for plasma generation are a known source of etch rate non-uniformity. For example, a magnetic field parallel to the plane of substrate undergoing processing in the plasma volume is expected to induce non-uniformity in the azimuthal etch rate pattern with about 5% etch rate non-uniformity induced per Gauss of applied magnetic field. Thin film thickness variation and etch chamber hardware variation are also known to contribute to azimuthal etch rate non-uniformity.
The induced non-uniformity can be used to make adjustments to the azimuthal etch rate pattern using applied DC magnetic fields. These applied magnetic fields are relatively small (e.g., <20 Gauss or <10 Gauss, preferably ≤1 Gauss or ≤½ Gauss) and allow for localized corrections to the plasma processing such as etch rate to be made without significantly affecting other etch parameters (e.g. CD uniformity, substrate temperature). For example, the relatively small applied magnetic field also minimizes potential damage to circuits on a substrate being etched. Thus, when an azimuthal etch rate non-uniformity is detected in an etching process, such as those induced by film thickness variation, etch chamber hardware and the magnetic field of the plasma, a localized magnetic field above a substrate and generated from the substrate support can be used to make adjustments to an azimuthal etch rate pattern. Similar results can be obtained in other plasma processing such as plasma assisted deposition.
To apply such a localized magnetic field, at least one current carrying conductor (current loop) may be powered.
In order to generate small magnetic fields, a plurality of conductors 150 are laterally spaced across the substrate support and/or edge ring at locations suitable to generate applied magnetic fields effective to make corrections and/or adjustments to plasma processing such as an etch rate pattern. The conductors 150 may be located in a component such as an ESC ceramic, such as ceramic plate 60. The conductors 150 may be located in another component, such as baseplate 10. The conductors 150 may also be located in hardware adjacent the substrate support, such as an edge ring. Preferably, the current carrying conductors 150 are placed inside baseplate 10, such that any heat generated due to electrical current flow inside the conductors does not substantially alter the substrate temperature. If incorporated in baseplate 10, the conductors 150 are preferably wires with an electrically insulating sheath.
The current carrying conductor 150 may preferably comprise a wire, cable or conductive trace that is electrically isolated from its surroundings to ensure that the applied DC current only flows inside the conductor and not within the substrate support component in which it is embedded. Electrical isolation may be realized by providing a thin electrically insulating layer, or layers, surrounding current carrying conductor 150. For example, if current carrying conductor 150 is disposed in a component that is electrically conductive, a thin layer, or layers, of electrically insulating material or sheath is disposed around the conductor for electrical isolation. The electrically insulating material may comprise a Kapton film, an epoxy film, a silicone film and combinations thereof. If current carrying conductor 150 is disposed in a component that is electrically non-conductive, a thin layer, or layers, of electrically insulating material or sheath is not required for electrical isolation. The material of conductor 150 preferably comprises copper, but may be comprised of other materials with a suitable electrical conductivity.
The conductor 150 may be disposed within a component of a substrate support such that it forms a current loop 150. The current loop 150 may be formed into any desirable shape within the component and with reference to the plane of the upper surface of the substrate 70 and is preferably circular or semi-circular. Other shapes may be oval, semi-oval, square, rectangular, trapezoidal, triangular or other polygonal shape. If a wire is chosen for conductor 150 to be incorporated in ceramic plate 60, a wire may be placed at a desired location in a mold containing powder starting materials of the component. The molded component is then fired to form the component. If a conductive trace is chosen for conductor 150, a powder starting material of the trace may be formed into a pattern in a powder molding, with subsequent firing of the molding to form the component. If a conductive trace is chosen for conductor 150 and is to be placed on an outer surface of a component, a metal or other material may be plated on the component, with subsequent etching of the metal or other material to form the current loop on the component. If an individual wire is chosen as the conductor 150 and is to be formed on an upper surface of a component, a groove may be machined into the surface with dimensions suitable for receiving the wire and the insulated wire can be mounted in the groove with a suitable adhesive.
The current loop 150 can be supplied DC power by electrical leads connected thereto.
A current loop, or loops, may comprise a single turn. However, a current loop, or loops, comprising a plurality of turns to form a coil, or coil-like, structure are also contemplated. The coil, or coil-like, structure may reduce the DC current required for generating the applied magnetic field during an etching process. The embodiments of the current loop, or loops, are preferably disposed in planes parallel to the substrate. However, the current loop, or loops, may be disposed in planes that are not parallel to the substrate if such a disposition is desired.
The dimensions of current carrying conductor 150 are not particularly limited so long as the dimensions render its applied magnetic field effective to make corrections and/or adjustments to the plasma to achieve uniform processing such as an azimuthal etch rate pattern. The length of current carrying conductor 150 may be chosen such that the corresponding current loop 150 may be shaped into a desired form. For example, if a 300 mm diameter wafer is to be etched, each localized magnetic field can be generated by a single circular shaped current loop formed with a loop diameter between about 1-150 mm and preferably between about 1-75 mm. Depending on the shape of the current loop and the desired number of currently loops in the substrate support, the length of an individual current loop may be 5-1000 mm, e.g., 5-50 mm or 50-1000 mm, such as in the case of a component comprising up to two hundred current loops. The diameter of current carrying conductor 150 itself is also not particularly limited and may be any diameter or dimension that forms a suitable applied localized magnetic field. For example, if a 300 mm diameter wafer is to be etched, the current loop may be a wire with a diameter of between about 0.5 mm-10 mm and preferably between about 0.5 mm-5 mm. If a conductive trace is to be the current loop 150, the trace may be formed in a rectangular shape with a thickness of between about 0.5 mm-10 mm, preferably between about 0.5 mm-5 mm, and a width of between about 0.5 mm-10 mm, preferably between about 0.5 mm-5 mm. The direction of current flowing in the current loop is not particularly limited and may be either clockwise or counter-clockwise. Preferably, the current flowing in current loop 150 is adapted to be reversible to switch the direction of the current flow, and thus, switching the direction of the applied DC magnetic field, if desired.
For purposes of explanation,
The number of current loops 150 that the substrate support assembly 100 comprise may be greater than two, such as that shown in
The current loops can be incorporated in any type of substrate support which may or may not include an electrostatic clamping arrangement, heating arrangement and/or temperature controlled baseplate. In a preferred method of controlling and/or adjusting an etch rate pattern using a substrate support incorporating current loops, a substrate is supported on a substrate support comprising a baseplate, a thermal insulating layer disposed over the baseplate, a heating plate disposed over the thermal insulating layer, a ceramic plate disposed over the a thermal insulating layer; and current loops; etching a substrate disposed on the substrate support; detecting an etch rate non-uniformity, such as an azimuthal etch rate non-uniformity, after etching has been initiated; and providing one or more of the current loops with DC power to generate localized DC magnetic fields that correct and/or adjust the etch rate non-uniformity.
An azimuthal etch rate non-uniformity may be detected as follows. A substrate comprising a thin film, such as a polysilicon thin film in the case of semiconductor substrate, to be processed is inspected to determine the thickness of the thin film at various locations across the substrate using standard interferometry techniques. The substrate is then plasma etched, or partially etched. After etching, or partial etching, the thickness of the thin film is measured again using standard interferometry techniques. The difference between the two thin film thickness measurements is determined by an appropriate algorithm, which also is able to generate an etch pattern on the substrate surface. From an etch rate pattern, a mean depth of the film thickness left on the substrate is determined, along with other parameters, such as the standard deviation and global maximum and minimum depths. These parameters are used to determine where selective application of a magnetic field can be applied to correct and/or adjust an azimuthal etch rate non-uniformity during subsequent etching of a batch of wafers undergoing the same etch process.
Alternatively, incoming wafer thickness of a substrate can be measured, the B-field pattern to provide uniform etching can be determined, and etching of a batch of substrates can be carried out. In another method, a substrate can be etched, an azimuthal pattern for etching can be determined, the magnetic field compensation is determined and further substrates are etched while applying the magnetic field compensation. The etch rate or other parameters could be monitored during plasma etching and the current loops could be powered to compensate for local etch rate variation during the plasma etch process.
Example 1A silicon wafer with a 1 μm thick silicon oxide film on its surface to be etched to a depth of about 400 nm is surrounded by an edge ring with two current loops, similar to the configuration of
Etching the remaining portions of the film on substrate 70 is then carried out. During the subsequent etching, DC power is supplied to the current loops 150 disposed in edge ring 110. DC power is supplied such that an 3 Gauss magnetic field is generated by the loops 150. After completion of etching, the etch rate pattern is determined, as described above. This etch results in an average of 189.5 nm of film thickness removed, with a three-sigma standard deviation of 13.9 nm (7.3%). The difference between a global maximum and minimum is 25.2 nm (13.3%). Analysis of the etch rate pattern is shown in
Thus, etching a substrate in the presence of an applied DC magnetic field can compensate for etch rate non-uniformity and thus provide a more uniform etch rate. With an applied magnetic field of about 3 Gauss generated from current loops in an edge ring, azimuthal etch rate non-uniformity can be decreased by about 3.3.% (range after partial etch—range after final etch), with a decrease in the three-sigma standard deviation of about 2.7% (deviation after partial etch —deviation after final etch). Furthermore, application of an 3 Gauss magnetic field shows that areas etched at a faster etch rate in the partial etch can be etched at a slower etch rate in the final etch step, thus, correcting for an azimuthal etch rate non-uniformity. Similarly, application of an 3 Gauss magnetic field shows that the areas that are etched at a slower etch rate in the partial etch can be etched at a faster etch rate in the final etch step, thus, correcting for an azimuthal etch rate non-uniformity.
Example 2In a process scheme to compensate for etch rate variation:
a. a wafer is partially etched and the etch rate non-uniformity is measured;
b. apply a magnetic field pattern to the plasma above a wafer (based on historical knowledge);
c. etch another wafer, determine etch pattern sensitivity to the applied magnetic field pattern since the applied field is known; and
d. optionally repeat steps a-c to determine an optimal magnetic field pattern.
Example 3In a process scheme to compensate for incoming wafer thickness variation:
a. measure incoming wafer thickness variation;
b. apply a magnetic field pattern (based on historical knowledge);
c. etch a wafer, determine etch pattern sensitivity to the applied magnetic field pattern since the applied field is known; and
d. optionally repeat steps a-c and adjust the applied magnetic field pattern if necessary.
All of the above-mentioned references are herein incorporated by reference in their entirety to the same extent as if each individual reference was specifically and individually indicated to be incorporated herein by reference in its entirety.
While the invention has been described with reference to preferred embodiments, it is to be understood that variations and modifications may be resorted to as will be apparent to those skilled in the art. Such variations and modifications are to be considered within the purview and scope of the invention as defined by the claims appended hereto.
Claims
1. A component of a substrate support assembly useful for supporting individual semiconductor substrates undergoing plasma processing, the component comprising:
- an electrostatic chuck for supporting a semiconductor substrate during plasma processing thereof or an edge ring which surrounds the semiconductor substrate, wherein the electrostatic chuck includes an embedded electrode receiving a first voltage to electrostatically attract the semiconductor substrate to the substrate support assembly; and
- a plurality of current loops incorporated in the electrostatic chuck or the edge ring, the plurality of current loops being laterally spaced apart and extending less than halfway around the electrostatic chuck or edge ring, each of the plurality of current loops being a wire formed into a loop;
- one or more DC power sources electrically connected to the plurality of current loops; and
- a controller configured to:
- supply the first voltage to the embedded electrode;
- supply a DC current to the plurality of current loops from the one or more DC power sources, the DC current directly supplied to the plurality of current loops being separate from and in addition to the first voltage supplied to the embedded electrode; and
- control the one or more DC power sources such that each of the plurality of current loops is independently operable and generates a localized DC magnetic field above the semiconductor substrate supported on the electrostatic chuck when the DC current is applied to a current loop of the plurality of current loops during plasma processing of the semiconductor substrate to adjust or correct the plasma processing of the semiconductor substrate
- wherein the localized DC magnetic field generated by the plurality of current loops does not generate plasma.
2. The component of claim 1, wherein the electrostatic chuck includes a baseplate, a thermal insulating layer above the baseplate, and a ceramic plate with the embedded electrode above the thermal insulating layer; and the plurality of current loops are embedded in the baseplate or the ceramic plate such that the plurality of current loops lie substantially in a plane parallel to an upper surface of the semiconductor substrate.
3. The component of claim 1, wherein the plurality of current loops are embedded in the edge ring such that the plurality of current loops lie substantially in a plane parallel to an upper surface of the semiconductor substrate.
4. The component of claim 1, wherein the plurality of current loops includes up to 200 current loops that have the same size and a circular shape and that are embedded in the electrostatic chuck or the edge ring.
5. The component of claim 1, wherein each of the plurality of current loops has a circular, semi-circular, oval, semi-oval, square, rectangular, trapezoidal, triangular or polygonal shape.
6. The component of claim 1, wherein the wire has a diameter of between about 0.5-10 mm.
7. The component of claim 1, wherein a periphery of each current loop of the plurality of current loops is laterally offset from a periphery of an adjacent current loop of the plurality of current loops.
8. A plasma processing chamber incorporating the component of claim 1, wherein the electrostatic chuck includes a heater layer having a plurality of heaters laterally distributed across the electrostatic chuck and operable to tune a spatial temperature profile for critical dimension (CD) control, the plurality of current loops including at least 9 current loops distributed laterally across the electrostatic chuck and operable to compensate for local non-uniformity in processing on the semiconductor substrate.
9. The plasma processing chamber of claim 8, wherein the plasma processing chamber is a plasma etching chamber.
10. The plasma processing chamber of claim 8, wherein the controller is configured to control the one or more DC power sources such that the one or more DC power sources supply the DC current to the plurality of current loops at the same time or different times with the same or different levels of the DC current, and wherein the DC current flows in the plurality of current loops in the same direction or different directions.
11. A method of controlling and/or adjusting a magnetic field pattern during plasma processing of the semiconductor substrate undergoing processing in the plasma processing chamber of claim 8, comprising:
- a) supporting the semiconductor substrate on the electrostatic chuck;
- b) plasma processing the semiconductor substrate; and
- c) supplying at least one of the plurality of current loops with the DC current to generate the localized DC magnetic field in a region above the semiconductor substrate so as to compensate for local non-uniformity in processing.
12. The method of claim 11, further comprising supplying the plurality of current loops with different amounts of the DC current, with the DC current travelling in a clockwise direction in each of the plurality of current loops.
13. The method of claim 11, further comprising supplying the plurality of current loops with different amounts of the DC current, with the DC current travelling in different directions in some of the plurality of current loops.
14. The method of claim 11, wherein each of the plurality of current loops generates the localized DC magnetic field above the semiconductor substrate with a field strength of less than 1 Gauss.
15. The method of claim 14, wherein the field strength is less than 20 Gauss or less than 0.5 Gauss.
16. The method of claim 11, wherein the plurality of current loops includes at least two current loops, and wherein the electrostatic chuck is surrounded by an edge ring having the at least two current loops, with each of the at least two current loops arranged on an opposite side of the edge ring.
17. The method of claim 16, wherein the plurality of current loops includes at least four current loops; wherein the edge ring has the at least four current loops, with each of the at least four current loops arranged diametrically opposite to another one of the at least four current loops; and wherein each of the at least four current loops has a circular, semi-circular, oval, semi-oval, square, rectangular, trapezoidal, triangular or polygonal shape.
18. The method of claim 11, wherein the plasma processing is plasma etching and further comprising, after steps a) and b) and prior to step c):
- removing the semiconductor substrate from the plasma processing chamber;
- detecting an etch-rate non-uniformity in an etch-rate pattern on the semiconductor substrate; and
- modifying step c) so as to compensate for film thickness induced etch-rate non-uniformity, etch chamber induced etch-rate non-uniformity or plasma induced etch-rate non-uniformity.
19. The method of claim 11, wherein the DC current is supplied from the one or more DC power sources comprising a multiplexed power scheme.
20. The method of claim 11, wherein the electrostatic chuck is adapted to support the semiconductor substrate having a diameter of at least about 200 mm, at least about 300 mm or at least about 450 mm.
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Type: Grant
Filed: Sep 16, 2011
Date of Patent: Aug 20, 2019
Patent Publication Number: 20130072025
Assignee: Lam Research Corporation (Fremont, CA)
Inventors: Harmeet Singh (Fremont, CA), Keith Gaff (Fremont, CA), Brett Richardson (San Ramon, CA), Sung Lee (Pleasanton, CA)
Primary Examiner: Benjamin Kendall
Assistant Examiner: Mirza Israr Javed
Application Number: 13/234,473
International Classification: H01F 7/20 (20060101); H01J 37/32 (20060101); H01L 21/67 (20060101); H01L 21/311 (20060101);
